Stereoscopic (three-dimensional or 3D) image display technology is technology that displays a 3D image as if the object actually exists in 3D space. 3D image display technology is expected to lead the next generation of display devices as a new concept in realistic image display technology improving on the level of planar visuals.
A 3D effect is realized via a procedure in which the left and right images of an object, perceived by the left and right eyes, are processed by the brain. Since a person's eyes are spaced apart by about 65 mm, they see images in two slightly different directions. At this time, a 3D effect is realized due to the optical phenomenon such as binocular disparity.
In order to display a 3D image, a 3D image display device may use a method of displaying stereoscopic images (3D image), that are slightly different images seen by an observer's respective left and right eyes. Such stereoscopic images can be displayed by way of the use of an eyeglasses method and an eyeglasses-free method. The methods for viewing a 3D image without wearing glasses include a parallax barrier method and a lenticular lens method. The parallax barrier method implements binocular disparity through a light shield layer having a structure in which barriers are regularly attached to the front or rear surface of a display panel. The lenticular lens method implements binocular disparity by using a small and regular semicylindrical lens called a lenticular lens. The two methods are advantageous in that glasses are not required; however, they are disadvantageous in that the effective viewing angle in which to obtain a 3D effect is significantly narrow, allowing only a single person to view a 3D image, and it is difficult to convert a 2D image into a 3D image.
The methods of viewing a 3D image while wearing glasses can be roughly divided into a shutter glasses method and a polarized glasses method. According to the shutter glasses method, the left-eye image and the right-eye image as displayed on a screen are alternately transmitted to each eye by the shutter glasses. An observer is able to separately recognize the left-eye image and the right-eye images alternately displayed on the screen due to the shutter glasses, and a 3D effect is obtained as the observer processes the two different images within his or her brain. However, the 3D display device using the shutter glasses method is disadvantageous in that the use of the shutter glasses increase the price of the product and an observer is directly exposed to electromagnetic waves generated by the driving of the shutter glasses.
According to the polarized glasses method, a patterned polarizer is mounted on an image display device. An observer experiences a 3D effect as a left-eye image and a right-eye image, having different polarization characteristics, are transmitted through the polarized glasses. The polarized glasses method is disadvantageous in that an observer must wear the polarized glasses, but is advantageous in that limitations on the viewing angle are small and the manufacturing thereof is easy.
The 3D image display device using the polarized glasses method may further include an optical film (optical filter) on the front surface of a screen display unit of a display device. As disclosed in U.S. Pat. No. 5,327,285, an optical film used in a 3D display device using the polarized glasses method, an optical film in which the right-eye image display unit and the left-eye image display unit are alternately disposed parallel to each other, is manufactured by coating a photoresist on a polarizing film in which a tri acetyl cellulose (TAC) film and an iodized stretched poly vinyl alcohol (PVA) film are laminated, exposing a predetermined portion, and by treating the exposed portion with a potassium hydroxide solution so that the function of phase difference of the predetermined portion is removed. Meanwhile, Korean Patent Application No. 2000-87186 discloses a method for manufacturing a 3D image display device. According to this patent application, a transparent substrate is coated with a birefringent material, and the birefringent material is subsequently partially exposed to light through a mask, thereby obtaining an optical filter (optical film) having portions in which chiral characteristics are modulated and portions in which original chiral characteristics are maintained, both of which are alternately arranged.
However, the manufacturing method disclosed in U.S. Pat. No. 5,327,285 is problematic in that it entails a complicated manufacturing step due to chemical etching, has high manufacturing costs, and has low productivity. The polarizing filter manufacturing method disclosed in Korean Patent Application No. 2000-0087186 is problematic in that it is actually somewhat difficult to control the chiral characteristics of the retarding material by using the intensity of light, resulting in low yield and instability according to temperature.
Therefore, there is a need for a method in which an optical filter for a 3D image display device with excellent process efficiency and productivity can be manufactured.